The present invention relates to an IGBT (Insulated Gate Bipolar Transistor) which is suitable for forming bidirectional switches.
The invention lies in the field of semiconductor circuits.
Commercially available IGBTs can be used to construct bidirectional switches which are used e.g. in converters, by each IGBT being connected in series with a diode. In this case, the forward direction of the diode corresponds to the switchable current direction of the IGBT. This circuit therefore effects blocking in the reverse direction. However, high on-state losses have to be accepted with this. U.S. Pat. No. 5,608,237 describes a bidirectional semiconductor switch comprising IGBTs in which IGBT structures are formed on two mutually opposite main sides of a semiconductor body. The dimensioning of such proposals for bidirectionally blocking switches is in each case chosen in such a way as to produce an NPT component (Non Punch Through). A triangular field profile builds up in the component under blocking loading. Other symmetrically blocking components such as e.g. thyristors or GTOs likewise have a non-punch-through dimensioning. That requires the component to have a large thickness and thus increases the switching and on-state losses in relation to the thinner punch-through dimensioning.
The invention provides a power semiconductor switch that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and that is simpler in construction and that can block high voltages in both directions.
In the case of the component according to the invention, a conventional structure of a power semiconductor switch, e.g. of an IGBT, is provided with an additional buffer layer on the source side and dimensioned in such a way that, in an operating state in which the component effects blocking, at least in a range of high electrical voltages which are applied to source and drain, a space charge zone produced in the semiconductor body extends as far as the respective buffer layer in accordance with a punch-through dimensioning. By virtue of the buffer layers present on both sides, the advantage of punch-through dimensioning (small thickness of the component) is combined with the advantage of non-punch-through dimensioning (possibility of symmetrical blocking capability).